You would need an obscenely large key size to make RSA post-quantum secure. The speedup a quantum computer gives you isn't some linear factor. People have explo

You would need an obscenely large key size to make RSA post-quantum secure. The speedup a quantum computer gives you isn't some linear factor. People have explored what that would look like: https://cr.yp.to/papers/pqrsa-20170419.pdf https://cr.yp.to/papers/pqrsa-20170419.pdf But more importantly: 1. No, quantum computers that big don't exist. 2. If they are somewhat practical, you really want perfect forward secrecy so they at least have to break a classically hard problem _every time_, which is unlikely with home-rolled RSA systems. 3. If you do care about post-quantum KEX (because your information needs to be secret for longer than you can count on quantum computers not being practical), we have faster alternatives, like SIDH.